Asthma is one of the four most common adult chronic disorders. It affects 7.3% (16.4 million) U.S. adults and costs $18 billion in direct healthcare costs and lost productivity. Control of symptoms and improving patient's quality of life (QOL) are the goals in asthma management and require patients to accurately identify their symptoms. But the low congruence between patients' symptom reports and their pulmonary function leads to disease management errors. The accuracy with which asthma patients recognize their symptoms is affected by emotional factors, and because high negative affectivity is related to low interoceptive accuracy and worse asthma symptoms and asthma physical health, the frequent mental distress prevalent among asthmatics is thought to result in difficulty in distinguishing symptoms of stress/distress from those of asthma. Mindfulness training teaches people to recognize and distinguish among the components of experience (thoughts, feelings, sensations/symptoms) and is associated with increased perceptual accuracy of respiratory resistance, and reduced affective negativity. It thus has the potential to improve patient's discrimination between asthma symptoms and stress/distress, resulting in improved asthma management, control and QOL. A pilot RCT (N=84) of a widely-available mindfulness training program (Mindfulness-Based Stress Reduction (MBSR)) to explore this hypothesis in adults with mild, moderate or severe persistent asthma. Intent to treat analyses comparing MBSR to an active control program showed clinically significant improvements in overall QOL (p=0.01), as well as important improvements in asthma symptoms (p=0.009), reduced use of asthma rescue medication (p=0.001), anxiety (p=0.05), perceived stress (p=0.01), and mindfulness (p=0.01). Promising improvements in the percentage of patients with well-controlled asthma also were found. All improvements were sustained 10 months post-intervention. Widespread adoption of this promising adjunct intervention will require sharper evidence regarding asthma control and symptoms. The primary aim of the proposed RCT is therefore to test MBSR against an active control on the key clinical outcomes of asthma control and symptoms using gold standard measures with 256 adults with mild, moderate or severe asthma. Secondary aims evaluate the program's effect on asthma QOL, lung function, cost-effectiveness, and the mediating effect of respiratory interoceptive accuracy on asthma control, QOL, and medication use. Assessments are at baseline, 6-, 12-, and 18-month follow-up. MBSR is available nationwide and covered by many third-party payers. If sustained and credible improvements in asthma control and symptoms are found, MBSR could be a useful adjunct to traditional medical treatment and would have the potential for improving the lives of people with asthma. By examining the mediating effects of psychosocial variables on asthma control, the study also generates new knowledge on mechanisms of change and maintenance in mind-body and behavioral programs in medicine.